This invention pertains to apparatus for separating solids from liquids, and more particularly pertains to apparatus employed for retrieval of relatively dense solid products or wastes from process liquids such as water, oils or solvents after the solids have settled therefrom. Specific examples include the retrieval of metal cuttings or filings from cutting oils, retrieval of dusts, fly ash or cinders from water circulated through a wet scrubber, removal of slag from water following quenching operations, and separation of compressible wastes such as sludges, asphalts or silts from process water tanks or waste water sumps.
More specifically, the present invention is an improvement in solids retrieval apparatus of the type which comprises an elongated, horizontally extending collector section which rests on the floor of a settling tank, an elongated, vertically extending conveyor or elevator section that is attached to one end of the collector section and has an upper discharge end above the pit or tank, and carrier means for conveying settled solids across the floor of the collector section and upwardly within the elevator section to the discharge end for retrieval of the solids from the tank. One version of such apparatus is described in U.S. Pat. No. 3,576,251, and it can be learned therefrom that retrieval of solids by such devices can be awkward, costly and inefficient as a result of improper design or operation. It is contended, for instance, that flights on the carrier means must be set and maintained in a proper disposition if they are to be effective in moving accumulated solids horizontally and then vertically out of the settling tank. Beyond this teaching, it has now been determined that the rate at which solids settle to the floor of the collector section is a factor which must be controlled, especially during peak or slug loading conditions when solids are settling from the liquid medium at a rate that is higher than normal, if overloading of the carrier means is to be prevented and removal of solids from the tank at a smooth and uninterrupted rate is to remain unhampered.
It should be noted, for instance, that the device disclosed in U.S. Pat. No. 3,576,251 does not include provisions for controlling the rate at which settling solids are delivered to the carrier means for conveyal across the floor of the collector section and up the elevator section. More specifically, the apparatus disclosed in the aforementioned patent comprises a medial, horizontally extending plate which resides above the floor of the collector section and provides a sought frictional drag on the flights of the carrier, and even though the plate may be perforated, the width thereof is not as great as that of the floor, and open spaces thus exist between the lateral edges of the plate and the sidewalls of the collector. It has been observed that during slug or peak loading conditions the settling of solids to the floor of the collector system remains largely unimpeded as a result of these open side spaces, and that there is little or no regulation of the rate at which settling solids are delivered to the carrier for controlling the loading thereof, nor hence for maintaining retrieval of solids from the tank at a smooth and uninterrupted rate.